Containers manufactured by biaxial stretch blow molding are extensively spreading. As a material of the containers, a thermoplastic polyester is used. For example, containers made of polyethylene terephthalate (PET) have excellent transparency or surface glaze, and also includes impact resistance, rigidity, gas barrier properties, and others required for liquid containers. Therefore, the containers are extensively utilized as containers for beverages, seasonings, and others.
A biaxial stretch blow molding method usually has a supply step, a blow molding step, a cooling step, a release step, and others (see, e.g., Patent Documents 1 and 2). Hence, the above containers are manufactured through these steps.
At the supply step, a previously heated preform is supplied into an opened mold. Furthermore, after the preform is supplied, the mold is closed.
At the blow molding step, heated blow air is supplied into the preform while a stretch rod is stretching the preform in an axial direction. As a result, the preform is expanded and stretched in a circumferential direction. The biaxially stretched preform comes into contact with a cavity surface of the mold to define its shape as a container.
At the cooling step, the biaxially stretched container is cooled. Usually, cooling air is supplied into the container to effect cooling.
At the release step, the molded container is taken out from the mold. At this time, for example, the stretch rod is retracted and the mold is opened.
FIG. 13 is a block diagram showing a blow air supply unit for a blow molding machine according to a conventional example.
As shown in this drawing, the blow air supply unit usually includes a high-pressure air source 101, a high-pressure gate valve 102, a heat exchanger 103, a switchover valve 104, and others. This blow air supply unit supplies heated blow air into a preform.
The high-pressure air source 101 generates blow air having a high pressure (e.g., 4 MPa).
The high-pressure gate valve 102 is provided on a downstream side of the high-pressure air source 101, and opens/closes a blow air channel. The high-pressure gate valve 102 is usually a high-pressure solenoid valve. An opening/closing operation of this high-pressure solenoid valve in a high-pressure air channel is assured.
The heat exchanger 103 is provided on a downstream side of the high-pressure gate valve 102 to heat blow air.
The switchover valve 104 is provided on a downstream side of the heat exchanger 102 to switch the blow air channel or a cooling air channel. A temperature gauge 105 measures a temperature of blow air at an outlet of the heat exchanger 103.
It is to be noted that cooling air is supplied from a high-pressure air source 106 for cooling air.
FIG. 14 is an explanatory drawing showing a switchover pattern of the switchover valve.
As shown in this drawing, the switchover valve 104 has a plurality of (e.g., five) ports. The switchover valve 104 opens/closes these ports to supply blow air or cooling air. For example, it opens ports 1, 3, and 4 and closes ports 2, and 5 at a blow molding step. When such an operation is performed, heated blow air is supplied into a preform (a container). Further, this valve opens the ports 2 to 5 and closes the port 1 at a cooling step. When such an operation is performed, cooling air is supplied into the container.
Patent Document 1: Japanese Patent Application Laid-open No. 133714-1989
Patent Document 2: Japanese Patent Application Laid-open No. 74319-1990